With the development of technology, many display devices such as mobile phones, panel computers begin to have fingerprint identification functions. In an existing display device as shown in FIG. 1, a backlight source 72 is arranged at a light entrance side of the liquid crystal display panel 71. The liquid crystal display panel 71 comprises a first substrate 51 (a substrate away from a light exit side) and a second substrate 52 (a substrate close to the light exit side) which are assembled. A plurality of light sensing units 1 are arranged in the first substrate 51, and a light shielding layer 11 is arranged at a side of the light sensing unit 1 close to the backlight source 72. When a finger presses the second substrate 52, the light that penetrates the liquid crystal display panel 71 can be reflected back to the light sensing units 1. The valley 91 and the ridge 92 of the fingerprint reflect light differently, so the sensed signals (such as photocurrent) generated by the light sensing units 1 at positions corresponding to the valley 91 and the ridge 92 are also different. By comparing the sensed signal of each light sensing unit 1, it can be determined whether it corresponds to the valley 91 or the ridge 92 of the fingerprint, thereby obtaining a pattern of the fingerprint, so as to realize fingerprint identification.
However, many structures in the display device can cause reflection, and various positions of the backlight source 72 can emit light simultaneously, thereby rendering the actually reflected light path in the display device rather complex. For example, the light emitted by the backlight source 72 might be directly reflected to the light sensing unit 1 by the second substrate 52 before it reaches the finger, the light emitted to the same position of the finger might come from a plurality of different positions, and would be reflected to a plurality of different light sensing units 1 correspondingly. That is to say, the sources of the light received by each light sensing unit 1 are very complex, and it is difficult to determine which part thereof is reflected by the fingerprint corresponding to it, therefore, the noise in the generated sensed signal is large, so as to be difficult to perform an accurate fingerprint identification.